Press Release

Large Galaxies Stopped Growing 7 Billion Years Ago

By SpaceRef Editor
April 18, 2011
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Galaxies are thought to develop by the gravitational attraction between and merger of smaller ‘sub-galaxies’, a process that standard cosmological ideas suggest should be ongoing. But new data from a team of scientists from Liverpool John Moores University directly challenges this idea, suggesting that the growth of some of the most massive objects stopped 7 billion years ago when the Universe was half its present age. On Monday 18 April team member Claire Burke will present their work at the Royal Astronomical Society’s National Astronomy Meeting (NAM 2011) in Llandudno, Wales.

How galaxies form and then evolve is still a major unanswered question in astronomy. The sub-galaxy units thought to have merged to make galaxies are themselves associated with fluctuations in the density of material in the cosmos left over from the Big Bang and seen today as temperature ‘ripples’ in the cosmic background radiation.

To study galaxy evolution, the team, which also included Professor Chris Collins and Dr. John Stott (now at the University of Durham), looked at the most massive galaxies in the Universe, known as Brightest Cluster Galaxies (BCGs) and so called because of their location at the center of galaxy clusters, structures that typically contain hundreds of galaxies.

In the nearby Universe BCGs are elliptical in shape and are the largest, most uniform and most massive class of galaxies observed, with each galaxy having a mass equivalent to up to 100 trillion (100 million million) Suns. Like smaller elliptical galaxies, BCGs are composed of old red stars and are thought to have formed through mergers of the dense population of sub-galaxies that were found in the center of galaxy clusters. By studying how BCGs grow in size gives an insight into the formation and evolution of galaxies in general.

Measuring the sizes of BCGs has always been difficult as their outer regions are very faint. Burke and her team have overcome this by using long exposure images from the Hubble Space Telescope data archive that pick up the dimmer parts of these galaxies. The BCGs they studied are so distant that the light we detect from them left 7 billion years ago, so they appear as they were when the Universe was less than half its present age.

When they examined the Hubble images, the team found that these distant BCGs are almost the same size as their nearby counterparts and that these galaxies can have grown by at most 30% in the last 9 billion years. This is in line with other work by the same research group, but is quite unlike the observed development of ‘regular’ elliptical galaxies. More significantly, conventional simulations of the evolution of the Universe predict that BCGs should have at least tripled in size over that time.

Ms. Burke comments: “The lack of growth of the most massive galaxies is a major challenge to current models of the formation and evolution of large scale structure in the Universe. Our work suggests that cosmologists appear to lack some of the crucial ingredients they need to understand how galaxies evolved from the distant past to the present day.”

NAM 2011 Press Office:
(09:00-17:30 BST, 18-21 April only)
Conwy Room, Venue Cymru, Llandudno, Wales
+44 (0)1492 873 637, +44 (0)1492 873 638

Science Contacts:
Claire Burke
Astrophysics Research Institute
Liverpool John Moores University
+44 (0)151 231 2923; cell: +44 (0)770 918 7019

Dr. John Stott
Department of Physics
Durham University
+44 (0)191 334 3773

Media Contacts:
Dr. Robert Massey
Royal Astronomical Society
+44 (0)794 124 8035 (cell)

Anita Heward
Royal Astronomical Society
+44 (0)7756 034 243 (cell)


The Brightest Cluster Galaxy (BCG) appears as the orange arc in this Hubble Space Telescope image of galaxy cluster Abell 2218. Credit: NASA, ESA, and Johan Richard (Caltech, USA). Acknowledgement: Davide de Martin & James Long (ESA/Hubble)

Further Information

The results of this study have been accepted for publication in the Monthly Notices of the Royal Astronomical Society (Stott et al., 2011, MNRAS, 432).

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NAM 2011

Bringing together around 500 astronomers and space scientists, the RAS National Astronomy Meeting 2011 (NAM 2011: takes place from 17 to 21 April in Venue Cymru (, Llandudno, Wales. The conference is held in conjunction with the U.K. Solar Physics (UKSP: and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST: meetings. NAM 2011 is principally sponsored by the RAS and the Science and Technology Facilities Council (STFC:

The Royal Astronomical Society

The Royal Astronomical Society (RAS:, founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics, and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities, and represents U.K. astronomy nationally and internationally. Its more than 3,500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories, and laboratories as well as historians of astronomy and others.

The Science and Technology Facilities Council

The Science and Technology Facilities Council (STFC: ensures the U.K. retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange. The Council has a broad science portfolio including astronomy, particle astrophysics, and space science. In the area of astronomy it funds the U.K. membership of international bodies such as the European Southern Observatory.

Venue Cymru

Venue Cymru ( is a purpose-built conference center and theater with modern facilities for up to 2,000 delegates. Located on the Llandudno promenade with stunning sea and mountain views, Venue Cymru comprises a stunning location, outstanding quality, and exceptional value: the perfect conference package.

SpaceRef staff editor.